Output driver circuits, or simply “drivers,” transmit electronic signals onto various forms of communication channels, including transmission lines, cables, printed circuit board traces, or the like. Receivers on the opposite ends of the channels sense the electronic signals. There are many types and classes of drivers and receivers, each offering a combination of traits that make it more or less suitable for particular applications. For example, a “single-ended” (SE) driver transmits an information signal as a varying voltage or current signal over a single conductor; a single-ended receiver recovers the information by comparing the signal to a reference. The main alternative to the single-ended approach is differential signaling, in which a differential driver transmits information as complementary signals over a pair of conductors, and a differential receiver compares the complementary signals to recover the data. Single-ended communication circuits are simpler and less expensive, whereas differential circuits offer relatively higher noise tolerance.
Communication circuits and the signaling schemes they support are not limited to differential or single-ended signaling. There are other classes of signaling, and many species of the various classes. Integrated-circuit (IC) vendors can design their ICs to include drivers and receivers optimized for a specific application, but often prefer to address a larger market by supporting multiple signaling schemes. For example, newer IC processes produce smaller transistors, which use less power and area while nevertheless providing improved speed performance. Newer IC designs may therefore support faster, more efficient signaling schemes. Unfortunately, the small transistors that support higher performance and reduced cost and area may be damaged by the higher voltages employed by older signaling schemes, and so may not be compatible with legacy devices and legacy signaling schemes. IC vendors thus prefer that their IC's include communications circuits that offer both the speed performance of state-of-the-art processes and legacy support for older communication schemes. The resulting circuits can be complex, area-intensive, and expensive, and one or more of the supported signaling schemes may suffer reduced performance as compared with a tailored solution. There is therefore a need for improved multi-modal drivers and receivers.
The figures are illustrations by way of example, and not by way of limitation. Like reference numerals in the figures refer to similar elements.